What is the standard deviation of the data set? 5,9,11,4,8,9,12

2.7
2.9
3.0
8.2

Which steps could be part of the process in algebraically solving the system of equations, y+5x=x^2+10 and y=4x-10

Write two point-slope equations for the line passing through the points (6, 5) and (3, 1)

Scores on the cognitive scale of the bayley-scales of infant and toddler development range from 1 to 19, with a standard deviation of 3. calculate the margin of error in estimating the true mean cognitive scale score, with 99% confidence, if there are 12 infants and toddlers in a sample.